•Mg/SiO2 catalysts are active for dehydrochlorination of 1,1,2-trichloroethane.•Catalysts with Mg(NO3)2·6H2O and MgCl2·6H2O as the precursors had identical performances.•A high yield of cis-dichloroethene (83.7%) was obtained on a stable 10Mg(N)/SiO2−300 catalyst.•Mg(OH)Cl is regarded as the active site for the reaction.

A series of Mg catalysts supported on SiO2 were prepared by an incipient wetness impregnation method and tested for gas phase dehydrochlorination of 1,1,2-trichloroethane. It was found that these catalysts were very active and selective for the reaction. The catalytic performance depended on the Mg loading rather than the Mg precursors as the catalysts using Mg(NO3)2·6H2O and MgCl2·6H2O as the precursors showed the similar performance. A catalyst containing 10 wt.% of Mg showed the best performance with a steady state TCE conversion of 92% and cis-dichloroethene selectivity of 91%. Moreover, characterizations of the catalysts revealed the formation of Cl-containing Mg species on the surface during the reaction. The analyses of the compositions of the stable catalysts under working conditions indicated a Cl/Mg ratio of 1, suggesting that Mg(OH)Cl could be the active sites for the reaction.